Exploring a $$\Sigma _{c}\bar{D}$$ state: with focus on $$P_{c}(4312)^{+}$$

Stimulated by the new discovery of $$P_{c}(4312)^{+}$$Pc(4312)+ by LHCb Collaboration, we endeavor to perform the study of $$P_{c}(4312)^{+}$$Pc(4312)+ as a $$\Sigma _{c}\bar{D}$$ΣcD¯ state in the framework of QCD sum rules. Taking into account the results from two sum rules, a conservative mass range $$4.07{\sim }4.97~\text{ GeV }$$4.07∼4.97GeV is presented for the $$\Sigma _{c}\bar{D}$$ΣcD¯ hadronic system, which agrees with the experimental data of $$P_{c}(4312)^{+}$$Pc(4312)+ and could support its interpretation as a $$\Sigma _{c}\bar{D}$$ΣcD¯ state.

A mesonic analog of the deuteron

Using the LAMP model for nuclear quark structure, we calculate the binding energy and quark structure of a B meson merging with a D meson. Our variational calculation shows that a molecular, deuteron-like state structure changes rather abruptly, as the separation between the two mesons decreases, and at a separation of about 0.14 fm, the hadronic system transforms into a four-quark bound state, although one maintaining an internal structure rather than that of a four-quark "bag." Unlike the deuteron, pion exchange does not provide any contribution to the ≈ 150 MeV binding.

Double pomeron exchange at the CERN Intersecting Storage Rings and $Sp\bar{p}S$ Collider

The CERN Intersecting Storage Rings, with [Formula: see text] from 22 GeV to 63 GeV and [Formula: see text], allowed the first observations of p + p → p + X + p with two leading protons (xF > 0.95) or two rapidity gaps Δy > 3. Studies of the central hadronic system (X) were made to search for glueballs, finding f0 and f2 resonances, and to advance our understanding of hadronic diffraction. I review the experiments, not including those at the Split Field Magnet (SFM) facility covered elsewhere in this volume. Some double pomeron exchange studies at the CERN [Formula: see text] Collider are also covered.

VECTOR MESON PRODUCTION AT HERA

The diffractive production of vector mesons ep→eVMY, with VM=ρ0, ω, ϕ, J/ψ, ψ′ or ϒ and with Y being either the scattered proton or a low mass hadronic system, has been extensively investigated at HERA. HERA offers a unique opportunity to study the dependences of diffractive processes on different scales: the mass of the vector meson, mVM, the centre-of-mass energy of the γp system, W, the photon virtuality, Q2 and the four-momentum transfer squared at the proton vertex, |t|. Strong interactions can be investigated in the transition from the hard to the soft regime, where the confinement of quarks and gluons occurs.